Problems with Safari & Software Update in OSX 10.5.8

This is a longshot, but my friend had a problem with a recent FireFox update. It evidently enabled his system-wide web proxy (System Preferences -> Network -> Advanced -> Proxies -> Web Proxy). Some pages were loading, but others were having problems. I'm not sure why this would happen, but Safari and Software Update might have some issue with that. The solution was to disable this option in system preferences and in FireFox (which was re-enabling the proxy on launch). I wish I could give you more info on how he did this in FireFox, but I wasn't there when he did it. This might be unrelated, but maybe it'll help!